Modernize DotNetSdkLocationHelper and hostfxr interop.

[teo-tsirpanis]

• The NativeMethods class was updated to use the P/Invoke source generator, and [UnmanagedCallersOnly]. The changes made are in a similar vein to Use UnmanagedCallersOnly in AssemblyDependencyResolver. dotnet/runtime#119034.
• The DotNetSdkLocationHelper class was updated to use APIs added in newer frameworks, like the regex source generator, or APIs to resolve symlinks. The latter also lets us remove the P/Invokes to libc.

[YuliiaKovalova]

hi @teo-tsirpanis
please resolve the conflicts and I will review it

[teo-tsirpanis]

@YuliiaKovalova conflicts resolved.

[rainersigwald]

No, wait, something is wrong:

❯ .\samples\BuilderApp\bin\Debug\net8.0\BuilderApp.exe .\MSBuildLocator.sln
Sample MSBuild Builder App 1.9.7+e4c2ece661.

Process terminated. Assertion failed.
   at Microsoft.Build.Locator.NativeMethods.hostfxr_resolve_sdk2_callback(hostfxr_resolve_sdk2_result_key_t key, Void* value) in S:\work\MSBuildLocator\src\MSBuildLocator\NativeMethods.cs:line 63
   at Microsoft.Build.Locator.NativeMethods.<hostfxr_resolve_sdk2>g____PInvoke|4_0(Void* __exe_dir_native, Void* __working_dir_native, hostfxr_resolve_sdk2_flags_t __flags_native,  __result_native)
   at Microsoft.Build.Locator.NativeMethods.<hostfxr_resolve_sdk2>g____PInvoke|4_0(Void* __exe_dir_native, Void* __working_dir_native, hostfxr_resolve_sdk2_flags_t __flags_native,  __result_native)
   at Microsoft.Build.Locator.NativeMethods.hostfxr_resolve_sdk2(String exe_dir, String working_dir, hostfxr_resolve_sdk2_flags_t flags,  result) in S:\work\MSBuildLocator\src\MSBuildLocator\obj\Debug\net8.0\Microsoft.Interop.LibraryImportGenerator\Microsoft.Interop.LibraryImportGenerator\LibraryImports.g.cs:line 19
   at Microsoft.Build.Locator.NativeMethods.hostfxr_resolve_sdk2(String exe_dir, String working_dir, hostfxr_resolve_sdk2_flags_t flags, String& resolved_sdk_dir, String& global_json_path) in S:\work\MSBuildLocator\src\MSBuildLocator\NativeMethods.cs:line 36
   at Microsoft.Build.Locator.DotNetSdkLocationHelper.<GetInstances>g__GetSdkFromGlobalSettings|4_2(String workingDirectory) in S:\work\MSBuildLocator\src\MSBuildLocator\DotNetSdkLocationHelper.cs:line 153
   at Microsoft.Build.Locator.DotNetSdkLocationHelper.GetInstances(String workingDirectory, Boolean allowQueryAllRuntimes, Boolean allowAllDotnetLocations)+MoveNext() in S:\work\MSBuildLocator\src\MSBuildLocator\DotNetSdkLocationHelper.cs:line 82
   at Microsoft.Build.Locator.MSBuildLocator.GetInstances(VisualStudioInstanceQueryOptions options)+MoveNext() in S:\work\MSBuildLocator\src\MSBuildLocator\MSBuildLocator.cs:line 389
   at System.Linq.Enumerable.WhereEnumerableIterator`1.ToList()
   at BuilderApp.Program.Main(String[] args) in S:\work\MSBuildLocator\samples\BuilderApp\Program.cs:line 26

[rainersigwald]

It is getting called twice, the first time with resolved_sdk_dir = 1, the second with 3. That appears to be newer than the docs describe

https://github.com/dotnet/runtime/blob/925205d06d82ce5e0d24e4e313fd66887fe89795/src/native/corehost/fxr/hostfxr.cpp#L225-L249

Maybe the assertions should be moved inside the switch @teo-tsirpanis?

[teo-tsirpanis]

Removed assertions, as per the other native callback.

[rainersigwald]

Fantastic, thank you!